StaffType as well as having the att

StaffType as well as having the attributes defined within the CREATE TYPE, also includes
the inherited attributes of PersonType, along with the associated observer and mutator functions
and any specified methods. In particular, the clause REF IS SYSTEM GENERATED
is also in effect inherited. In addition, we have defined an instance method isManager that
checks whether the specified member of staff is a Manager. We show how this method can
be used in Section 28.4.8.